A conventional micro-fluid ejection device such as an ink jet printhead generally has flow features either formed in a thick film layer deposited on a semiconductor substrate containing ink ejection devices or flow features ablated along with nozzle holes in a polymeric nozzle plate material. The term “flow features” is used to refer to fluid flow channels, fluid ejection chambers, and other physical features that provide a fluid such as ink to ejection devices on the semiconductor substrate. When both the nozzle holes and flow features are ablated in the nozzle plate material, a thick film material is typically not present. A disadvantage of forming the flow features and nozzle holes in the nozzle plate material is that the flow feature height and nozzle bore length are constrained by the nozzle plate material thickness. For micro-fluid ejection heads having a separate thick film layer and nozzle plate with the flow features formed in a thick film layer, the nozzle bore length is constrained to equal to the nozzle plate material thickness and the flow feature dimensions are determined by the thickness of the thick film layer.
With a trend toward increasing the functionality of micro-fluid ejection devices, it is desirable to provide fluid ejection devices on a single semiconductor substrate for ejecting different fluids having different drop masses. However, for largely disparate drop masses, the above constraints make the design of a single semiconductor substrate for multiple fluids difficult. For example, smaller droplet masses may be accommodated using flow features ablated in a nozzle plate material of a particular thickness. However, the larger droplet masses require additional flow features that cannot be ablated in a nozzle plate material suitable only for smaller drop masses. Alternatively, larger droplet masses may be accommodated using flow features formed in a thick film layer with nozzles ablated in a nozzle plate. However, the combined thickness of the thick film layer and nozzle plate degrades the ejection efficiency of the smaller droplet masses ejected from the same semiconductor substrate.
As the speed of micro-fluid ejection devices such as ink jet printers, increases the frequency of fluid ejection by individual ejection actuator elements must also increase requiring more rapid refilling of fluid ejection chambers. The requirement for more rapid refilling provides an incentive to devise a novel approach to providing flow features suitable for fluid ejection actuators for multiple size droplet masses on a single semiconductor substrate. Hence, there exists a need for improved micro-fluid ejection devices and methods for making the devices.